Impact Loads on Retaining Walls

[nwong]

I've come accross many situations where I have a vehicle guard rail attached or directly adjacent to the top of the a (concrete/masonry/steel) retaining wall. Most of the time they're along drives and parking lots within a site.

AASHTO Section 2 says to use a 10kip load over 5ft for concrete barriers. This increases the size of the retaining wall significantly.

AASHTO Section 3 states that impact loads are not to be included for the design of retaining walls, foundation pressures, or footings except for the portions above grade.

What is the correct way to apply impact loads onto retaining wall?

Thanks

 

[broekie]

How I have done this sort of thing in the past is to assume that the impact load propogates through the wall at a 45 degree angle (1 on 1 slope).

In other words, let's say you had a 10' tall wall. To find the moment at the base of the wall, I would assume that this 10 kip load acted over 5' (from AASHTO) + 10' + 10' (from 1 on 1 slope) = 25' of length. The moment at the base would then be 10 kips / 25' * 10' = 4 ft-kips (per foot of wall).

This would be instead of 10 kips / 5' * 10' = 20 ft-kips (per foot of wall), which is quite high like you mentioned.

I really think that this is a valid assumption. The 10 kips over 5' is for the structural design of the barrier, bot the wall that the barrier is sitting on top of.

Hope this helps.

 

[LicensedToPEe]

The deformation of the raling can decrease the momentum of the impacting object (vehicle) and thus reducing the magnitude of the moment at the base of the wall.